Stabilizing device for two-stroke free piston engines



Nov. 2, 1937. G. J. P. J. J. BRUN STABILIZING DEVI [CE FOR TWO-STROKEFREE PISTON ENGINES 3' Sheets-Sheet .1

Filed June 19, 1935 Jive afar: eogeg kazfizfnzkjiciag fas'ep/l firm?Nov. 2, 1937.

G. J. P. J. J. BRUN STABILIZING DEVICE FOR TWO-STROKE FREE PISTONENGINES Filed June 19, 1935 s Sheets-Sheet 2 Nov. 2, 1937. G p. J BRUN2,097,431

STABILIZING DEVICE FOR TWO-STROKE FREE PISTON ENGINES Filed June 19,1955 3 Sheets-Sheet 3 xiiw hwgm Patented Nov. 2, 1937 FREE PISTONENGINES Georges Jean Pierre Jules Joseph m St.

Etienne, France Application June 19, 1935, Serial No. 27,292 In FranceJune 20. 1931 15 Claims.

This invention relates to a stabilizing and regulating device for freepiston engines, particularly,

adapted for compressed gas generators, in which the working andcompressor pistons are arranged in tandem on the same rod, and in whichthe entire combustion energy is used for actuating the compressor.

In the construction of free piston engines and particularly of motorcompressors of the aforementioned type, the problem of the continuityand of the stability of the working pistons gives rise to considerablediiiiculty, such as during a single stroke of the movable member of theengine, the driving work produced on one of the pistons balances theresisting work produced on the other. At the end of each stroke acertain amount of energy is collected in pneumatic form inthe free spaceof the cylinders. The pneumatic energy at the end of a stroke and thekinetic energy at mid-stroke are approximately equal to the driving workper stroke.

Any change of this work, such as is never avoided in internalcombustion" motors, reacts immediately on the velocity of the movablemember of the engine and on the compression of the gas at the end of astroke; consequently on the subsequent working of the motor.

The working of double-acting motor compressors, such as comprisedouble-acting and two stroke working and compressor pistons is difllcultto stabilize.

In motors with a high compression, the volume of the combustion chamberis small with respect to the swept volume, so that a small increase ofthe stroke causes a considerable increase of the compression ratio andof the driving work. In

order to stabilize the working, the resisting work of the compressormust be raised at least in the same proportion-the compressor must beadapt- 40 ed therefore for high delivery pressures and provided withwide'free spaces at the end of the stroke, resulting in a low volumetricefllciency.

The stability of double-acting motor-compressors with a deliverypressure ranging from 4.to 5 kgs.

is always rather unsatisfactory, and a singlespark failure is frequentlysufllcient to cause their stopping.

In single-acting motor-compressors, comprising single acting two-strokeworking and compressor 60 pistons, in which the working surfaces areopposite one another, a proper practical stability may be ensured byactuating the reverse stroke of the working piston towards the cylinderhead by means of the combined action oi a pneumatic 55 recuperator andof a compressor with a wide free space. Such constructions disclose,however, numerous difllculties, such as the moving member is made heavy;the average velocity is reduced; the specific losses oi the recuperatorreduce the efliciency of the compressor.

It has also been suggested to connect the common rod of the working andcompressor pistons with a fly-wheel by means of a rod and crank system.Such an arrangement, however, depriv es the device of its essentialcharacter of a 0 free-piston engine and renders it similar to ordinarymotor-compressors. Moreover, it necessitate's providing a rotating shaftand large and heavy rods, adapted to ofler a sumcient mechanicalresistance to the violent and irregular strains 15 caused by thedifferent laws of motion of the rods and of the piston device. Thisresults in a great inertia, which precludes elevated linear velocitiesof the pistons, which form one 0! the advantages of the free pistonmotors. 2

The 'obiect of my invention is to obviate the store-said diillculties.

The invention is characterized in that a rotating shaft, provided with afly-wheel is connected with the rod carrying the pistons by means of a25 hydro-elastic transmission, comprising a doubleacting auxiliarypiston, -(or two opposite singleacting pistons), termed a recuperatorpiston, mounted on said rod, and moving inside a cylinder, filled withoil, constantly communicating, 30 at each of its ends, on one hand witha container provided with an automatic feeding device, and on the otherhand, with one or several bores, in which movepistons, connected bymeans of connecting rods with the cranks 0! said rotating 35 shalt.

The relation of the volume swept by each surface of the recuperatorpiston with the totalv volume swept by the corresponding rod controlledpistons is superior to 1, and equal to 2. The 40 volume of eachcontainer being selected in a manner, that the relation of the workproduced on the recuperator piston during a single stroke, by theexpansion of the liquid compressed in said recuperator, and by the rodconnected pistons, 45 and 01 the driving work produced during a singlestroke on the piston 01 the movable member, should be of a sufiicientvalue, preferably approaching 1.

This device gives the free piston engine as satisfactory a regularityand stability as those 0! an engine with red controlled pistons andmoreover lightens the engine and increases the speed of the pistons. Italso facilitates the control of the distributing devices, which isparticularly difli- I v g lcult in free piston engines with high pistonvelocity.

Itisknownthatifthepistonvelocityofs motor is doubled, and the velocityof the gaseswhen passing through the apertures is maintained constant,the maximum kinetic energy of the .valves is multipled by 22. Engineswith high piston velocity therefore require particularly powerfulcontrols, but in free piston motors, a rotating shaft, which ispractically indispensable in such cases, is not provided. The deviceaccording to the invention also greatly facilitates, owing to thehydro-elastic coupling with a driving shaft, the starting of suchengines, which is generally diiilcult owing to the high value oftheimpulsion necessary for starting their movable member.

One embodiment of the" invention is hereinafter described, by way ofexample, and illustrated in the accompanying drawings.

rigurelisadiagram ofthedeviceaccording to the invention;

Figure 2 is an elevatlonal view of the engine in axial section;

Figure 3 is an axial sectional view of the stabilizing device shown inFigure 2, but provided with various improvements.

Figure 1 shows an engine comprising a working cylinder l and acompressor cylinder l, inside which move respectively the working pistonI: and compressor piston ls, keyed in tandem on a rod l1.

This rod also carries a third piston is, moving in a cylinder 2, whichhas no communication with the others. This cylinder will hereinafter bereferred to as a recuperator cylinder. The recuperator cylinder isfilled with a compressible liquid, such as oil, and is in constantcommunication at each of its ends, on one hand with the isolatedcontainers 3 and 4, equally filled with oil, and, on the other hand, bymeans of plpings 31 and 41 with the cylinders la and la, in which movethe pistons 5 and 6, connected by means of rods 5: and 5a with theopposite cranks 5: and 53, of a crank-shaft carrying a fly-wheel 8. Thisshaft is coupled by means of a clutch 8 with an electric starter Ill,and controls, by means of bevel pinions II, a distributing shaft II; itcarries moreover a centrifugalgovernor M.

The motor-compressor having been started by means of the starter III,the crank-shaft and the fly-wheel are driven at the speed of the motor,the dead points of said shaft coinciding with those of the movablemember, while the elasticity of the hydraulic transmission constitutedby cylinders 2, 33, 43 and pistons i4, 5 and 6 as described aboveeliminates strong strains on the connecting rods and on the shaft.Therefore the engine may be constructed lightly. If, for some reason, adisturbance is caused in the working of the compressor, the dead pointsof the rod ii are shifted in respect of those of the rod-controlledpistons 5 and 6, but the recuperator piston is is then subjected tothrusts from the fly-wheel 8, by means of the compressed liquid, saidthrusts tend ng to synchronize its motion and to avoid thus exaggeratedshifts between the dead points a of said rod and pistons. If thedisturbance persists, the velocity of the rotating shaft is increased orreduced according to the name of the disturbance, and the regularity ofthe working is then reestablished by the governor. Speed regulation bygovernors of this type will be found described in Dyke's Automobile andGasoline Engine Encyclopedia, 16th Edition, published the apparatus,the

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Flgmelisageneralviewinsectionof vices curing the hy movable member ofthe free formedbyarodinattheendsof keyed the working and compremor arenot illustrated in thh film). piston i4. movable in the bore ofcylinder2,isalsoiixedonsaidrod Ir. Thebose oithe cylinderl'isinconatantatitsrighteniwiththecontaincr .andby meansoftheconduitsliandiawith boresI: and 84. At its left permanent communication and, by means of conduits4; ends of the bores 41 and cylinder 2, the containers 8 and l l13:,1-3, and 'the m constantly filled with a erally with oil.

The bores 84 and l: on one 3:, on the other, are respectively co-axialtheir heads are opposed. A double-acting I is connected by means of theetc-had the connectingrods I: with the crankthe crank-shaft 1. Adouble-acting moving in the bores I: means of the croashead 01 the rods6:, with the crank-pin The crank-pins is and O: are keyed at oneanother, so that the bores 31 andJ4 are displaced tion in respect of thedirection being opposite to moving in the bores: and

The engine illustrated in with a shaft. comprising tw should beunderstood that it may four, six, or eight such crank-pins, the value ofthe power exchange engineshaft and the rod one half of said crank-pinsbeing at in respect to the other half. The shaft 1 carria a fly-wheel ibe connected by means starting motor II; the engine is easily bythrowing in gear the motor II with 'I; said shaftissetintormflmsmfllealternating motion of the rod is the pistons. When the stroke of saidmovable member attains a sufllcient value for causing in the workingcylinder the compression required for ignition, the fuel issin'lmlntolideyllndesand therod l1 carryingthephtonsthendrivesthe shaft1, at normal speed.

The shaft 1 is 5% iii iiii is 8 z igi i let'the liquid supplied throughthe pipe I! penetrate into the containers but prohibitits reversemotion. The pipe I! is connectedwith a tank containing oil at lowpressure.

The constructive characteristics of the hydroelastic coupling are:

1. The volumes 1: and v swept respectively by the left and right facesof the recuperator piston;

2. The volumes V and V of the containers 4 and 3. The volumes w and wswept by the sets of rod-controlled pistons communicating respectivelywith the left and right faces of the recuperatom-piston.

The volumes 1: and v are always greater respectively than the volumes asand w.

The working of the device varies slightly according to whether themotor-compressor is double or single acting.

In a double-acting compressor. the forces applied to the movable member,during a simple stroke, are the same, whether said member moves fromleft to right or from right to left.

Therefore:--v=v' When the engine is working permanently at normal speed,the work produced on the workingpiston in a simple stroke balances theresistant work of the compressor piston. As the shaft rotates insynchronism, the dead points of the movable member coincideautomatically with those of the rod controlled pistons. When, forexample, the recuperator piston is at the end of its stroke towards theleft, the rod controlled pistons moving in the bores 43 and 44 are atthe end of their stroke in the direction opposite to'the heads of saidbores. The pressure of the liquid on the right side of the recuperatorpiston is reduced to a. minimum and is brought automatically to thevalue of the pressure in the conduit it, which approaches 0.

On the left side of the recuperator piston, the pressure rises to avalue p, resulting from the compression, in the container of a volumeequal to V, of the volume vw, that is of the excess of the volumedischarged by the recuperator piston over the volume admitted behind therod controlled pistons. A

At the next simple stroke, the pressure on the left side of the.recuperator piston falls from p to (i, and that on the right side ofsaid piston rises from O to p. The action of the recuperator on themovable member of the compressor is similar to that of a very powerfulspring, and the kinetic energy of said movable member at mid-stroke isincreased by pv is one part of which, equal to n ma being provided bythe work of the rod-controlled pistons during the single halt-stroke,and the rest equal to p (12-10) by the expansion of the compressed oilin the containers.

The fly-wheel slows the motion during the first half of the singlestroke, accelerates it during the second half, and possesses at the endof said stroke the same kinetic energy as at the start.

In the occurrence of a disturbance, the work on the working pistonbecomes higher or lower than the resistant work of the compressorpiston, and the dead points of the movable member are shifted in respectof those of the rod-controlled pistons, being in advance in the firstcase and late in the second. Calculation shows that almost no changeoccurs in the stroke of the movable member and in the compression.

The shifting of the dead points produces at mid-stroke maximum workingpressure, in opposite directions on both sides of the recuperatorpiston. This pressure slows the motion of the movable member, when thedriving work exceeds the resistant work, and accelerates said motion inthe opposite case. Conversely, this pressure accelerates or retains themotion of the fly-wheel, which provides automatically the supplementarywork required for bringing the device back to equilibrium. If thedisturbance continues, the speed of the shaft is accelerated or reduced,and equilibrium is then established by the governor.

The essential data of a hydro-elastic coupling are:

1. The relation w of the volume swept by the recuperatorpiston and thatswept by the rod controlled pistons;

2. The relation or the work transmitted at mid-stroke by the recuperatorpiston to the movable member and the driving work t per single stroke.

If the relation W approaches 1, the coupling is insui'iiciently suppleas the motion of the rod-controlled pistons is practically sinusoidal,whereas that of the movable member is not sinusoidal, as itsacceleration at the dead points is generally much-greater than that of asinusoidal motion of same frequency and amplitude. This produces, inadditionto the oil compression froin one dead point to the other, theoccurrence of pressure variations of multiple frequency. the amplitudeof which depends eventuaily on the relation If v is almost equal to 10,these pressure variations will be of considerable amplitude, and the rodcontrolled pistons will be practically directly member. The efforts andfactors of wear at the articulationsvof the rod-crank transmissions areincreased and the crank-shaft has to be very strong to provide anappropriate factor of safety.

J If, on the contrary, w is but a small fraction of v, the connection istoo elasticand the shifts between the dead points of the rod-controlledpistons and those of the movable member, in case of unbalancing, are toowide; if the shift of the cranks articulated on the controlled pistonsis greater than when the movable member is at dead point, the workingbecomes unstable, and the crank-shaft falls out of step.

Similarly, if the ratio I t v is very high, the shifts between thedead-points in case of disturbance are small, but the energy provided bythe controlled pistons, before and after the dead point is high, and thecrank-shaft required for transmitting this work with an appropriatesafety is very cumbersome. If, on the contrary, the ratio fallin thevalues of These different necessities are met by selecting in a suitablemanner the afore-mentioned relations. By way of example if and v in:

r the shifts of the cranks at the dead points of the movable member donot exceed 30"; in the worst of cases, i. e. in case of a complete sparkfailure, the fly-wheel provides the entire driving work.

On the other hand, if v=2w, the amplitude of the pressure variations ofhigher frequency is smaller in respect of p, and the hydro-elasticcoupling of a motor-compressor with elevated compression and with apiston velocity approaching 20 metres persecond does not require morethan 4 crank-pins.

If the motor-compressor is single-acting, its working is practically thesame, with the following exceptions, supposing that in a single-actingengine'the working face of the working piston is directed to the left,and the working face of the compressor piston to the right:

1. The strains applied to the movable member during a single stroke fromleft to right, that is an expansion stroke, are different from thoseduring a stroke from right to left, namely a com pression stroke.

2. The energy accumulated at the end of the expansion stroke is reduced,owing to the absence of the pneumatic recuperator, to the energyaccumulated in the free space of the compressor, which is generallyconsiderably smaller than the energy accumulated at the end of thecompres-- sion stroke in the free space of the working cylinder. Thehydro-elastic coupling enables a very simple working of the engine inthese circumstances; it is suilicient to give the volumes v, V', toslightly higher values than those of volumes v, V,'w, so that themovable member is retained by the recuperator during the expansionstroke, and receivesa thrust from said recuperator during thecompression stroke, whereas the energy provided in this case, which isequal to ing, at the end of an expansion stroke, the necessary energyfor producing further compression. In that case the volumes 1), V, w areequal respectively to v, V, w, as in the double-acting engine.

The movable member of a single-acting engine is always possessed with ahigher velocity at the middle of the expansion stroke than at the middleof the compression stroke. This causes the dead points of the movablemember to be shifted at permanent normal working in respect to those ofthe controlled pistons; the dead point of the movable member, at the endof the compression stroke, is late, whereas it is in advance at .the endof the expansion stroke. By selecting suitably these shifts may bereduced to a few degrees, and

locity of same.

the working of the single-acting engine becomes thus almost similartothatof the double-acting member during the normal working of the engine,said fly-wheel intervening thus only in the occurrence of disturbances.

As explained above, the pressure on a controlled piston, duringpermanent working, rises from 0 to a maximum value p, when said pistonpasses from its dead point adjacent to the cylinder head to its oppositedead point. The object of the device hereinafter described is to balancesaid pressure by the reaction of .an auxiliary hydraulic recuperator.

An engine, provided with controlled pistons and with such a device isillustrated in section in Figure 3 of the accompanying drawings.

This figure illustrates, similarly to Figure 1, at h-h,and at 3H4, thebores connected respectively with the left and right heads of therecuperator cylinder, which is notillustrated in Figure l; the pistons 5and 6, moving in these bores, are keyed on rods 54, 64, which aremovable insideguiding rings 5s, 8s mortised at the ends of said bores.The spaces between the pistons and the guiding rings are filled with acompressible liquid and communicate respectively, for

the pistons moving in the bores 43 and 44 with a container l8, and forthe pistons moving in the bores 33 and -34, with a container I9, saidcontainers being also filled with oil. These containers are providedvwith automatic feeding valves 20, 2|, similar to the valves l6, l1illustrated in Figure 2. When the pistons 5 and 6 move away from theheads of the bores 4:, 44, they compress, towards the guiding rings, theliquid in the container l8, bringing its pressure from near to 0 to avalue p". Simultaneously the pressure on the opposite face of thepistons rises from 0 to p. The volume of the container l8 and thepressure p" are selected in a manner that the value of the latter on theface of the piston turned towards the guiding ring should balance thepressure p exerted on the opposite piston. Similarly the volume of thecontainer 19 is selected in a manner to balance the pressures on thepistons moving in the bores 33 and 34. Practically no strain is thusexerted on the pistons i and 6 as long as the dead points of the movablemember coincide with those of the controlled pistons. The only forcetransmitted to the crank-pins of the shaft is the inertia of the memberspossessed with alternating motion.

Moreover the auxiliary recuperators may be easily set to balance thisforce of inertia.

- When the working is disturbed, the dead points of the movable memberand of the controlled pistons are shifted; the controlled pistons arethen subjected solely to the maximum working pressure at mid-stroke,which ensures the transmission of a certain permanent work from thefly-wheel to the movable member, or vice versa.

The auxiliary recuperators ensure the balancing except for a determinedstroke. of the movable member, that is for a determined ve-Partlcularly, this balancing is not produced at the starting of .theengine, when the pressures existing in the principal recuperator arevery low. In order to avoid abnormal strains on the transmission at thestarting, an automatic device is provided for discharging the auxiliaryrecuperators. At normal working, the pressure in theauxiliary'recuperator is in a determined relation pII m:-

with the pressure in the principal recuperator; the discharge isperformed automatically as soon as the relation between the pressures inthe auxiliary and principal recuperators rises above m. For that purposethe container l 8 communicates with the head of the bore 4:, that iswith the principal recuperator, by means of bores 22 and 23, in whichmoves a differential piston, subjected on its face 14 to the pressure ofthe principal recuperator, on its face 25 to the pressure of theauxiliary recuperator, and on its annular face 2! to the feedingpressure, which is near to 0.

When the relation of the pressures in the auxiliary and principalrecuperators exceeds the relation of the diameters of the faces 26 and25, which is adapted to be equal to m, the diiferential piston isdisplaced upwards, and connects, by means of grooves 21, the auxiliaryrecuperator with the exhaust. The auxiliary recuperators are thereforeautomatically emptied at the start of the first revolution. The feedingvalves subsequently insure a progressive filling. Their diameter beingcalculated in a manner, that the oil expelled at thefirst revolutiontakes some time before filling again the auxiliary recuperators.

What I claim is:-

1. In a two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod, adapted to move freelyinside said cylinders, a working piston and a compressor piston movablein said cylinders and keyed in tandem on said rod, a stabilizing de--vice, comprising a rotatable shaft, a fly-wheel on said shaft, and meansfor elastically connecting said shaft with said free rod.

2. In a two-stroke free piston engine, the combination comprising aworking cylinder, a

compressor cylinder, a rod adapted to move freely inside said cylinders,a working piston and a compressor piston movable in said cylinders andkeyed in tandem on said rod, a stabilizing device, comprising arotatable shaft, a fiy-wheel on said shaft, and means for elasticallyconnecting said shaft with said free rod, said means comprising ahydraulic transmission device.

3. In a two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable in saidcylinders, a working piston and a compressor piston movable insaidcylinders and keyed in tandem on said rod, a stabilizing device,comprising a rotatable shaft, a fiy-wheel on said shaft, and means forelastically connecting said shaft with said free rod, said meanscomprising a cylinder, termed recuperator cylinder, a double-actingpiston, termed recuperator piston, keyed on said free rod and movableinside said recuperator cylinder, subsidiary cylinders eachcommunicating with one end of said recuperator cylinder, pistons in saidsubsidiary cylinders, rods connecting said pistons with said rotatableshaft, containers for a compressible liquid each connected with one endof the recuperator cylinder, and means for maintaining said con tainers,recuperator cylinders and subsidiary cylinders constantly filled with acompressible liquid, the volume of said recuperator cylinder and that ofeach of said subsidiary cylinders being such, that the volume swept byeach face of the recuperator piston is at least equal to that sweptbysaid rod-controlled pistons movable in said subsidiary cylinderscommunicating respectively with said faces of the recuperator piston,and the volumes of said containers being such, that the work produced onthe recuperator piston, during a single stroke, by the expansion of theliquid compressed inthe recuperator cylinder and by said rod-controlledpistons is approximately equal to the driving work per single strokeproduced on the working piston of the engine.

4, In a two-stroke free piston engine, the combination comprising aworking cylinder, a com-, pressor cylinder, a rod freely movable in saidcylinders, a double-acting working piston and a double-acting compressorpiston movable in said cylindersand keyed in tandem on said rod, astabilizing device, comprising a rotatable shaft, a fly-wheel on saidshaft, a cylinder,termed recuperator cylinder, a double-acting piston,termed recuperator piston, keyed on said free rod and movable insidesaid recuperator cylinder, subsidiary cylinders of equal volumes, eachconnected with one end of said recuperator cylinder, pistons in' saidsubsidiary cylinders, rods connecting said pistons with said rotatableshaft, containers of equal volumes for a compressible liquid each set incommunication with one end of the recuperator cylinder, and means formaintaining said containers, recuperator cylinder and subsidiarycylinders constantly filled with a compressible liquid, the volume ofsaid recuperator cylinder and that of each of said subsidiary cylindersbeing such, that the volume swept by each face of the recuperator pistonis at least equal to that swept by said rod-controlled pistons movablein said subsidiary cylinders communicating respectively with said facesof the recuperator piston, andgthe volumes of said containers beingsuch, thatthe work produced on the recuperator piston during a singlestroke, by the expansion of the liquid compressed in the recuperatorcylinder and by said rod controlled pistons is approximately equal tothe driving work per single stroke produced on the working piston of theengine.

5. In a two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable insidesaid cylinders, a working piston and a compressor piston movable in saidcylinders and keyed in tandem on said rod, a stabilizing device,comprising arotatable shaft, a fly-wheel on said shaft, a startingdevice, means for. throwing said shaft in gear with said startingdevice, means for connecting said shaft elastically with said free rod,and

iary' cylinders constantly filled with said compressible liquid.

7. In a two-stroke free piston engine, a hydroelastic transmissiondevice comprising a recuperator cylinder, a recuperator piston in saidcylinder connectible with the free piston of said engine,

subsidiary cylinders each communicating with one end of said recuperatorcylinder, pistons in said subsidiary cylinders connectible with astabilizing device for the engine, subsidiary recuperators, eachconnected with the end of said subsidiary cylinders opposite to thatconnected with the principal recuperator cylinder, containers for acompressible liquid each communicating with one .end of said principalrecuperator cylinder, means for maintaining said containers, principalrecuperator cylinder, subsidiary cylinders and subsidiary recuperatorsconstantly filled with said compressible liquid and means forautomatically discharging said subsidiary recuperators when the relationof the pressures existing in said subsidiary recuperators and in theprincipal recuperator cylinder exceeds a predetermined value.

8. In a two-stroke free piston engine the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable in saidcylinders, a single-acting working piston and a single-acting compressorpiston, movable inside said cylinders and keyed in tandem on said rod, astabilizing device, comprising a rotatable shaft, a fly-wheel on saidshaft and means for elastically connecting said shaft with said freerod, said means comprising a cylinder, termed recuperator cylinder, adouble-acting piston, termed recuperator piston, keyed on said free rodand movable inside said recuperator cylinder, subsidiary cylinderscommunicating each with one end of said recuperator cylinder, pistons insaid subsidiary cylinders, rods connecting said pistons with saidrotatable shaft, containers for a compressible liquid eachcommunicatingwith one end of the recuperator cylinder, and means formaintaining said containers, recuperator cylinder and subsidiarycyllndersconstantly filled witha compressible liquid, the volume of saidrecuperator cylinder and that of each of said subsidiary cylinders beingsuch that the volume swept by each face of the recuperator piston is atleast equal to that swept by said rod controlled pistons movablein saidsubsidiary cylinders communicating respectively with said faces of therecuperator piston, and the volumes oi said containers being such thatthe work produced on the recuperator piston,

during'a single stroke, by ,the expansion of the liquid compressed inthe recuperator cylinder and by said rod controlled pistons isapproximately equal to the driving workper singlestroke produced on theworking piston of the engine, and the volumes swept by the two faces ofthe recuperator piston, the volumes of said containers, and the volumesswept in the subsidiary cylinders, corresponding to said two faces ofthe recuperator piston, by said rod controlled pistons, being such thatthe difference of the work produced on both sides of the recuperatorpiston, during a single stroke, is sufilcient to ensure the reversemotion of said rod, carrying the working and compressor pistons of theengine, during the compression tatable shaft, a fiy-wheel on said shaft,a hydroelastic coupling between said shaft and said rod comprising a,cylinder, termed recuperator cylinder, a double-acting piston, termedrecuperator piston, keyed on said free rod and movable in saidrecuperator cylinder, subsidiary cylinders communicating each with oneend of said recuperator cylinder, pistons moving in said subsidiarycylinders, rods connecting said pistons with said rotatable shaft, meansfor balancing the thrusts applied to said rod-controlled pistons by thepressure existing in said recuperator cylinder, containers for acompressible liquid, communicating each with one end of the recuperatorcylinder, and means for maintaining said containers, recuperatorcylinder and subsidiary cylinders constantly filled with a compressibleliquid.

10. In a two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable in saidcylinders, a working piston and a compressor piston movable inside saidcylinders and keyed on said rod, a stabilizing device, comprising arotatable shaft, afly-wheel on said shaft, a hydro-elastic couplingbetween said shaft and said rod comprising a cylinder termed recuperatorcylinder, a double-acting piston, termed recuperator piston, keyed onsaid free rod and movable in said recuperator cylinder, subsidiarycylinders each communicating at one end with one end of said recuperatorcylinder, pistons movable in said subsidiary cylinders, rods connectingsaid pistons with said rotatable shaft, containers, termed subsidiaryrecuperators. filled with a compressible liquid and each communicatingwith the end of one subsidiary cylinder situated opposite the endcommunicating with the principal recuperator cylinder, the volumes ofsaid subsidiary recuperators being such with respect to the volumesswept by said rod controlled pistons that the thrusts applied to saidpistons by the liquidcompressed in said subsidiary recuperators balance,at normal working, the thrusts applied to these pistons by the pressureexisting in the principal recuperator cylinder, as well as the inertiaof the members possessed with alternating motion, said stabilizingdevice comprising moreover containers for a compressible liquid eachcommunicating with one end of the principal recuperator cylinder, andmeans for maintaining constantly filled with a compressible liquid saidcontainers, principal recuperator cylinder, subsidiary cylinders andsubsidiary recuperators.

11. In a two-stroke free piston engine, the com bination comprising aworking cylinder, a com-- pressor'cylinder, a rod freely movable in saidcylinders, a working piston and a compressor piston movable inside saidcylinders and keyed on said rod, a stabilizing device comprising arotatable shaft, a fly-wheel on said shaft, a hydroelastic couplingbetween said" shaft and said rod comprising a cylinder termedrecuperator cylinder, a double-acting piston, termed recuperator piston,keyed on said free rod and movable in said recuperator cylinder,subsidiary cylinders, each communicating with one end of saidrecuperator cylinder, pistons movable in said subsidiary cylinders, rodsconnecting said pistons with said rotatable shaft, containers, termedsubsidiaryrecuperators, connected with the end of said subsidiarycylinders opposite to that connected with the principal recuperatorcylinder, means for automatically discharging said subsidiaryrecuperators when the relation of the pressures existing in saidsubsidiary recuperators and in the principal recuperator cylinderexceeds a determined value, containers for a compressible liquid eachcommunicating with one end of said principal recuperator cylinder, andmeans for maintaining said containers, principal recuperator cylinder,subsidiary cylinders and subsidiary recuperators constantly filled witha compressible liquid.

12. In a two-stroke free piston engine, the combination comprising aworking cylinder, 9, compressor cylinder, a rod freely movable in saidcylinders, a working and a compressor piston movable inside saidcylinders and keyed on said rod, a stabilizing-device, comprising arotatable shaft, a fly-wheel on said shaft, a hydro-elastic couplingbetween said shaft and said rod, comprising a cylinder, termedrecuperator cylinder, a double-acting piston, termed recuperator piston,keyed on said free rod and movable in said recuperator cylinder, twocylinder blocks, each comprising two bores with opposite heads,oommunicating at their ends adjacent to their heads respectively withthe opposite ends of the recuperator cylinder, double-acting pistons insaid cylinder blocks, two crank-pins on the rotatable shaft keyed at 180to one another, rods connecting said pistons with said crank-pins, twocontainers for a compressible liquid, each connected with one end of therecuperator cylinder, ballvalves in said containers adapted to let theliquid into said containers and to prevent its outflow therefrom, asupply-pipe of compressible liquid at low pressure connected with saidvalves.

13. In a two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable in saidcylinders, a working piston and a compressor piston movable inside saidcylinders and keyed on said rod, a stabilizing device comprising arotatable shaft, a fly-wheel on said shaft, ahydro-elastic couplingbetween said shaft and said rod comprising a cylinder, termedrecuperator cylinder, a double-acting piston, termed recuperator piston,keyed on said free rod and movable in said recuperator cylinder, twocylinder-blocks each com-.

prising two bores with opposite heads, communicating at their endsadjacent to their heads respectively with the opposite ends of therecuperator cylinder, a rod in each of said cylinder-blocks movable inthe bore thereof, pistons keyed on the ends of said rods, crank-pinskeyed on said rotatable shaft, rods connecting said crank-pins with saidpiston-carrying rods; rings mounted at the ends of said bores oppositetheir heads and adapted to guide said piston-carrying rods, containers,termed subsidiary recuperators each connected with the ends opposite theheads of two opposite bores situated in different cylinder-blocks, aball-valve in each of said subsidiary recuperators adapted to let theliquid into said recuperators and to prevent its outflow therefrom,containers for a compressible liquid each communicating with one end ofthe principal recuperator cylinder, ball-valves in said containersadapted to let the liquid into the containers and to prevent its outflowtherefrom, a supply-pipe of compressible liquid at low pressureconnected with the "elves of said containers and subsidiaryrecuperators. 14. In a two-stroke free piston engine, the combinationcomprising a working cylinder, a compressor cylinder, a rod freelymovable in said cylinders, a working piston and a compressor pistonmovable inside said cylinders and keyed on said rod, a stabilizingdevice comprising a rotatable shaft, a fly-wheel on said shaft, ahydro-elastic coupling between said shaft and said rod comprising acylinder, termed recuperator cylinder, a double-acting piston, termedrecuperator piston, keyed on said free rod and movable in saidrecuperator cylinder, two cylinder-blocks each comprising two bores withopposite heads, communicating at their ends adjacent to their headsrespectively with the opposite ends of the recuperator cylinder, a rodin each of said cylinder-blocks movable in both the bores of the block,pistons keyed on the ends of said rods, crank-pins keyed on saidrotatable shaft, rods connecting said crank-pins with saidpiston-carrying rods, rings mounted at the ends of said bores oppositetheir heads and adapted to guide said piston-carrying rods, containers,termed subsidiary recuperators each connected with the ends opposite theheads of two opposite bores situated in diiferent cylinder-blocks, aball-valve in each of said subsidiary recuperators adapted to let theliquid into said recuperators and to prevent its outflow therefrom,containers for a compressible liquid each communicating with one end ofthe principal recuperator cylinder, ball-valves in said containersadapted to let the liquid into the containers and to prevent its outflowtherefrom, a supply-pipe of compressible liquid at low pressureconnected with the valves of said containers and subsidiaryrecuperators, and means for automatically discharging said subsidiaryrecuperators when the relation of the pressures existing in thesesubsidiary recuperators and the principal recuperator cylinder exceeds adetermined value, said means comprising a subsidiary bore in eachcylinderblock, a differential piston in said bore comprising a largeface, asmall face, and an intermediate annular face, springs adapted tourge said differential pistons downwards, conduits connecting the largefaces of said pistons with the principal recuperator cylinder, theirsmall faces with the subsidiary recuperators, and their intermediateannular faces with the supply pipe of liquid at low pressure, therelation of the diameters of the large and small faces of saiddifferential pistons being equal to the determined value of the relationof pressures existing in the principal and subsidiary recuperators, atwhich the latter are to be discharged.

15. In a. two-stroke free piston engine, the combination comprising aworking cylinder, a compressor cylinder, a rod freely movable insidesaid cylinders, a working piston and a compressor piston movable in saidcylinders and keyed in tandem on said rod, a stabilizing devicecompris-.

ing a rotatable shaft, a fly-wheel on said shaft, and a centrifugalgovernor, and means for elastically connecting said shaft with said freerod.

GEORGES JEAN PIERRE JULES JOSEPH BRU'N.

